MR imaging is a medical imaging technique that uses an applied magnetic field and RF pulses to make images of organs and structures inside the body. During MR imaging, the magnetic field causes magnetic field vectors of protons (typically in hydrogen atoms) to align with the magnetic field. The RF pulses cause the magnetic field vectors of the protons to be displaced from the magnetic field and re-align with the magnetic field. An MRI scanner picks up signals from the protons in the body that result from the magnetic field vectors re-aligning with the magnetic field. The signals may then be converted into images based on the location and strength of the incoming signals.
The rotating frame is the coordinate system that rotates about Z axis at the Larmor frequency of the scanner. In the rotating frame, a magnetization vector rotating at the Larmor frequency in the laboratory frame appears stationary. T1rho (or “T-1-rho”) is the spin lattice relaxation time constant in the rotating frame, which determines the recovery of the longitudinal magnetization (along the effective field) in the presence of a “spin-lock” radio-frequency field and is an alternate MRI contrast method to visualize early pathological changes. T2rho (or “T-2-rho”) is the spin-spin relaxation time constant in the rotating frame, which determines the decay of the transverse magnetization (perpendicular to the effective field) in the presence of a “spin-lock” radio-frequency field and is an alternate MRI contrast method to visualize early pathological changes.